(617d) Formic Acid Electro-Oxidation over Graphene-Based Single Atom Catalysts: A Case Study on Coverage Effects

Direct formic acid fuel cells have been regarded as one of the most promising technologies for sustainable transportation and portable energy demands. Traditionally, platinum (Pt) and palladium (Pd) nanoparticles have been considered the most efficient catalysts for the formic acid oxidation (FAO) reaction. However, recent experimental work has illustrated that single-atom transition metals, namely iridium and rhodium, supported in nitrogen-doped graphene may act as a promising alternative for common FAO catalysts. These single-atom catalysts not only show unique catalytic performance relative to their bulk/nanoparticle counterparts, but they also display enhanced CO tolerance over Pd and Pt catalysts. To uncover the source of this catalytic behavior, we used first-principles density functional theory calculations to model a series of single-atom transition metal catalysts embedded in nitrogen-doped graphene. By modeling the FAO reaction on these different metal centers, we identify key descriptors for predicting catalytic performance. Using these insights, we identify novel systems which may also be active for FAO. More broadly, using formic acid electro-oxidation as a model reaction, we illustrate how “coverage” effects on 2D-materials impact catalytic performance. We explore the benevolent and sometimes detrimental implications these “coverage” effects can have on the active site of 2D single-atom catalysts. Our findings illustrate the importance of directly considering coverage effects on 2D single-atom catalysts and highlight conditions where coverage effects may be relevant.